1. Technical Field
The present invention relates to a vehicle seat belt system, and particularly relates to a seat belt system constructed to minimize belt tension acting on an occupant of a vehicle during non-emergency conditions.
2. Background Art
Vehicle seat belt systems which minimize belt tension acting on an occupant are well known. One such seat belt system is shown in U.S. Pat. No. 4,630,841. The seat belt system of U.S. Pat. No. 4,630,841 includes a number of detection switches for detecting the tension in seat belt webbing buckled around a vehicle occupant. These switches control a motor which in turn controls the biasing force of a spiral spring acting on a take-up shaft to wind up the belt webbing. By controlling the biasing force of the spiral spring, the belt tension acting on the occupant can be controlled.
Another known vehicle seat belt system is shown in U.S. Pat. No. 4,659,108. This seat belt system includes a slack sensor switch which changes between two states depending on whether there is slack in a seat belt or not. The system further includes a motor controlled in response to the state of the slack sensor switch. After the seat belt is buckled around a vehicle occupant, the motor rotates in a direction so as to tighten the seat belt against the occupant and then rotates in the reverse direction so as to pay out some seat belt to provide some slack in the seat belt. As a result, belt tension does not act on the occupant.
Also, there are numerous vehicle seat belt retractor designs which include a comfort mechanism. Typically, a comfort mechanism includes a first member fixed to a retractor spool on which belt webbing is wound. The spool and the first member are biased in a belt retraction direction by a belt rewind spring. A second member selectively blocks rotation of the first member and the retractor spool in the belt retraction direction. When rotation of the first member and the retractor spool is blocked, the biasing force of the belt rewind spring does not act through the belt webbing against the occupant. U.S. Pat. No. 4,854,522 discloses an example of such a seat belt retractor.